Re: one final observation on my piping to multiple processes.

[Larry Ploetz]

On 2/10/11 12:15 PM, Philip Rowlands wrote:
>
>
> One final note; the pee utility included in the moreutils package does
> exactly what you want without the funky shell syntax.
>
>
Funky syntax?!? I take exception to that, sir. ;-)

Larry "I *like* bash; I really do" Ploetz
--

  
*Larry Ploetz
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Re: one final observation on my piping to multiple processes.

[Philip Rowlands]

On 10/02/2011 14:23, McKown, John wrote:

The use of>(...) and tee seem to be what I need to pipe the output
from bzcat to muliple perl scripts. But I found a "bug" in my
original:

bzcat data*bz2| tee>(perl script1.pl) | perl script2.pl

The stdout from script1.pl is piped into script2.pl ater the bzcat'ed
data. So I need to do something like:

bzcat data*bz2 | tee>(perl script1.pl>/dev/fd/2)|perl script2.pl

that way the output from script1.pl is send to stderr instead of
stdout, and does not end up going into script2.pl.


A better model might be
$ a | tee >(b) >(c) >(d) > /dev/null

i.e. explicitly throw away tee's stdout. This doesn't upset b/c/d's
stdout as bash's process substitution occurs before the file
redirection. However don't depend too much on the order (or worse,
buffering) of the process-substitution stages' output.

Confusingly, pipelines are constructed in a different order, so this
behaves differently:
$ a | tee >(b) >(c) | d

by sending a, b and c's stdout to d's stdin.

One final note; the pee utility included in the moreutils package does
exactly what you want without the funky shell syntax.


Cheers,
Phil

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one final observation on my piping to multiple processes.

[McKown, John]

The use of >(...) and tee seem to be what I need to pipe the output from bzcat 
to muliple perl scripts. But I found a "bug" in my original:

bzcat data*bz2| tee >(perl script1.pl) | perl script2.pl

The stdout from script1.pl is piped into script2.pl ater the bzcat'ed data. So 
I need to do something like:

bzcat data*bz2 | tee >(perl script1.pl >/dev/fd/2)|perl script2.pl

that way the output from script1.pl is send to stderr instead of stdout, and 
does not end up going into script2.pl.

Again, many thanks for this neat way to reduce my run-time.

John McKown
Systems Engineer IV
IT

Administrative Services Group

HealthMarkets(r)

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